1. Field of the Invention
This invention relates to a color filter to be suitably used for a color television set or the display device of a personal computer and also to a method of manufacturing the same. More particularly, the present invention relates to a color filter having colored portions of the three primary colors by means of an ink-jet system. The present invention also relates to a liquid crystal element substrate using such a color filter and a liquid crystal element formed by using such a substract.
2. Related Background Art
The technological development in the field of personal computers in recent years, portable personal computers in particular, has produced an ever-increasing demand for liquid display devices, particularly for color liquid crystal display devices. However, the demand can be met only when such display devices are supplied at reduced cost. In more specific terms, there is a strong demand for less costly color filters that take a significant part in the overall cost of manufacturing display devices.
While efforts have been paid to meet the demand while satisfying the requirements for the performance of color filters, no technology has been established to satisfy the requirements. Firstly, typical known processes for preparing color filters will be discussed.
First, a dyeing process is known. With this process, a water-soluble polymeric material is formed on a glass substrate as material to be colored and then it is patterned to show a desired profile by photolithography. Thereafter, the obtained pattern is immersed in a dye bath to produce a colored pattern. This dyeing step is repeated three times for the three primary colors of red (R), green (G) and blue (B) to obtain a colored layer of R, G and B on the substrate.
Second, there is known a pigment dispersing process, which is most popular in recent years. With this process, a photosensitive resin layer containing a pigment in a dispersed state is formed on a substrate and then the layer is patterned to produce a mono-color pattern. Then, this pattern forming step is repeated three times to obtain a layer colored to the three primary colors of R, G and B.
Third, an electrodeposition process is known. With this process, a transparent electrode is formed on a substrate by patterning and a first color is produced by means of electrodeposition of immersing the patterned electrode into an electrodeposition coating solution containing a pigment, resin and an electrolyte. Then, this step of producing a color is repeated three times to form a colored layer of the three primary colors of R, G and B. Finally, the formed layer is baked to complete the process.
Fourth, there is known a process of dispersing pigments into thermosetting resin, repeating a printing operation three times for the three primary colors of R, G and B and curing the resin to produce a colored layer.
With any of the above listed processes, a protection layer is generally formed on the colored layer.
What is common to all the above listed processes is that a same step has to be repeated three times for forming a colored layer of the three primary color of R, G and B to consequently raise the manufacturing cost. Additionally, a manufacturing method involving a large number of steps is normally accompanied by a low yield. Furthermore, patterns that can be formed by an electrodeposition process are limited in terms of profile so that such a process cannot be applied without difficulty to active matrix type (so-called TFT type) liquid display devices comprising TFTs (thin film transistors). On the other hand, a printing process is not suited for finely pitched patterns because of the problem of poor resolution that accompanies the process.
Japanese Patent Application Laid-Open Nos. 59-75205, 63-235901 and 1-217302 propose methods of manufacturing a color filter by using an ink-jet system.
Methods of manufacturing a color filter by using an ink-jet system provide the advantages of:
(1) simpleness of the manufacturing process; PA1 (2) low manufacturing cost; and PA1 (3) a wide choice of colorants because dyes can be used. PA1 (A) poor heat resistance, and PA1 (B) high solubility to water and organic solvents. PA1 (A) When forming a protection layer on the colored portions of the color filter by spin-coating, the dyes contained in the colored portions can cause migration around the interface thereof due to the organic solvent contained in the protection layer. Then, the adhesion of the colored portions to the protection layer can be deteriorated and/or the protection layer can become colored. PA1 (B) When forming a transparent electro-conductive film on the colored portions, the dyes contained in the colored portions can become oxidized around the surface thereof because they are exposed to an oxygen- containing atmosphere at high temperature. When the dyes are oxidized, their color tones change and/or the contrast of the color filter can be degraded.
Dyes are much more abundant if compared with pigments so that desired colors can be reproduced almost freely depending on the application. Additionally, a color filter realized by using dyes normally provides a high contrast if compared with a color filter prepared by using pigments.
However, compared with pigments, dyes are normally accompanied by the problems of:
Thus, a color filter prepared by using dyes typically involves the following problems: